Mechanical motion rectifier leads to better energy harvesting

(Phys.org) -- Mechanical energy is all around us, whether in the form of a vehicle's vibrations, ocean waves, or vibrating train tracks. However, much of this energy is irregular and oscillatory - for example, road bumps cause a vehicle to move up and down at random intervals - but energy harvesting works best with regular, unidirectional motion. To address this problem, a team of engineers from the State University of New York (SUNY) at Stony Brook has developed a new type of energy harvester that converts irregular, oscillatory motion into regular, unidirectional motion, in the same way that an electric voltage rectifier converts AC voltage into DC. Among its applications, the energy harvester could be used in regenerative shock absorbers, which have the potential to save US drivers billions of dollars per year in fuel costs.

The engineers, led by SUNY Mechanical Engineering Professor Lei Zuo, have been working on energy harvesting devices for the past decade. Their regenerative shock absorber, which harvests a vehicle's vibrational energy that would otherwise be wasted as heat, can generate enough electricity to charge the vehicle's battery and power its electronics. By reducing the load on the alternator and engine, the device improves fuel efficiency by 2-8%, depending on the type of vehicle, vehicle speed, and road conditions. The shock absorber can be retrofitted in the suspension systems of cars, trucks, buses, and military vehicles, as well as installed on train tracks.

WIth the new ability to convert irregular vibrations into regular motion, the engineers predict that the benefits of this device could increase further.

We've developed a new type of energy harvester, based on a mechanism which I call mechanical motion rectifier (MMR), Zuo told Phys.org. It will convert the irregular oscillatory vibration into regular unidirectional rotation, just like the way that an electric voltage rectifier converts the AC voltage into DC. I believe it will solve the fundamental challenge of large-scale vibration energy harvesting due to irregular oscillations, and offers significant advantages of high efficiency and high reliability. Based on the MMR, we have recently developed and tested new energy harvesters for applications in vehicle suspensions, railroads, and ocean wave energy converters.

In prototype tests, the researchers achieved 60-70% efficiency with the MMR-based energy harvester. This advantage stems from several changes in the way that the new regenerative absorber harvests energy and generates electricity. For example, the new shock absorber's motion produces less friction and can produce direct current without electric diodes and a capacitor, which are usually required. Because of its smoother operation, the new absorber is also more reliable and less prone to damage compared with regenerative absorbers that operate with irregular reciprocating motion.

What does this mean for drivers? A typical car, for example, has an energy harvesting potential of 100-400 watts using the regenerative shock absorber. Since a car uses about 250-350 watts (not including optional accessories such as the radio), the researchers estimate a fuel savings of up to 4% in vehicles with internal combustion engines and up to 8% in hybrid vehicles. If just 5% of the vehicles in the US used the device, driving an average of one hour per day and saving 3% in fuel costs, drivers could save an estimated $1 billion of gasoline per year.

The researchers estimate that it would take 3-4 years to recoup the installation costs for conventional vehicles, and 2-3 years for hybrid and electric cars. Trucks and buses, due to their larger sizes, could recoup costs in just 1-2 years. Military vehicles could reap large benefits, as well, considering the cost of oil in Afghanistan is around $400 per gallon. As a side benefit, vehicles with regenerative shock absorbers would also have improved comfort and maneuverability since more of the vibrations are absorbed than normal.

By implementing the MMR design into energy harvesters attached to railroad tracks, hundreds of watts of vibrational energy can be harnessed from passing trains. With support from the US Department of Transportation and the New York State of Energy Research and Development Authority, the researchers are designing the MMR energy harvesters to power track-side electrical devices such as lights, crossing gates, and monitoring sensors, which could be especially valuable in remote areas. Zuo explained how both railroads and ocean wave energy applications could benefit from the MMR design in a similar way as vehicles.

The train-induced rail track vibrations are in pulse form and very irregular, he said. And ocean wave energy is concentrated at low frequencies and at low, alternating velocities. These irregular oscillatory motions make the vibration energy harvesting particularly challenging, much more than the wind energy, where the turbines rotate in one direction at relatively steady speed. The MMR directly converts the irregular oscillatory vibration into regular unidirectional rotation, therefore solving the fundamental challenge of vibration energy harvesting.

The engineers have recently taken steps toward commercializing the energy harvesting devices, having licensed the technology to a new company called Harvest Energy, which is co-founded by investment banker Henry Mariano. Already seeing some interest from bus and truck manufacturers, the team's next steps will involve marketing, commercial testing, and large-scale manufacturing.

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23 comments

For example, the new shock absorber's motion produces less friction and can produce direct current without electric diodes and a capacitor, which are usually required.

I know of no small electrical motor/generator that would produce direct DC without some sort of commutator, be it electronic (rectifiers) or mechanical (brushes). Brushed generators obviously have the disadvantage of wearing out.

And, the mechanics are quite clever but I'm still doubtful whether it'll actually last for years in operation because the ratcheting mechanism is bound to wear out over the sheer number of load cycles it experiences.

Just driving around for an hour with vibrations in the 100 Hz range will change the direction of the pinion gear over a million times. If there's any play or rattle between the gear teeth against the rack teeth, it's going to be jackhammering the gear and rack until either one breaks. Pretty much the same goes for the ratcheting mechanism.

I know of no small electrical motor/generator that would produce direct DC without some sort of commutator, be it electronic (rectifiers) or mechanical (brushes)...

Magnets and coils produce AC power, a full wave rectifier has no moving parts and is very reliable, routinely used in vehicle alternators there is nothing wrong with rectifiers.

Who needs mechanical parts that wear just use magnets and coils and a suitable low impedance sink matched to the main battery. The size of the magnets and number of coil turns manage the power/voltage produced, its quite easy to do it that way.

Afghanistan doesn't produce oil or gas and has no confirmed reserves of oil but, has reserves of natural gas, no export.

So Halliburton which 'successfully' supplies US military in Iraq also does (afaik) in Afghanistan & charges appropriately due to a multitude of factors lumped together as 'war risk'.

Eg.Halliburton charged the US for 'lease' of forklifts at Baghdad airport (which belong to Iraq government) at around $10,000/month or even more. ie. It would have been cheaper to buy new ones and ship them in each month !

Scandalous war profiteering and at the top !

"Cheney was chairman and CEO of Halliburton Company from 1995 to 2000", it's considered Cheney and/or family still has shares.

Recall Cheney presenting 'evidence' to the UN that Iraq had WMDs, incestuous & rather treasonable !

This is an absurtly unefficient, complicated and unreliable sollution. What's with all the mechanics? The same is achieved by using a permanent or electro magnet on the piston of the shock and a coil on the fixed side.

Magnets and coils produce AC power, a full wave rectifier has no moving parts and is very reliable, routinely used in vehicle alternators there is nothing wrong with rectifiers.

Which is exactly what the article claims they do without, when they say they don't need any "electric diodes and a capacitor".

That is a rectifier they're describing there. So what do they use if they're not using a rectifier? A mechanical commutator. The DC generator has carbon rods on springs that physically grind against a commutator shaft, that switches the current to always go in the same direction.

The only reason not to use an electronic rectifier is to avoid the forward voltage drop of the diodes, which makes for a significant efficiency loss, but if it means you have carbon rods grinding away mechanically, that's not really any better.

Which is exactly what the article claims they do without, when they say they don't need any "electric diodes and a capacitor".

Fed propaganda by some who cant conceive using rectifiers properly and use more parts with all the wear issues is an example of being manipulated by 'spin' as if its a positive. I concede its subtle & blatant misdirection beyond most people's experience but 'bad thinking' it is nonetheless.

Eikka showed his ignorance of rectifiers led to more bad thinking

..not to use an electronic rectifier is to avoid the forward voltage drop of the diodes, which makes for a significant efficiency loss..

They are not going to get a patent as there is so much prior art for this idea it's almost ridiculous.

Absolutely correct, though there are many odd ways I have seen patents drafted to try & obfuscate technical issues. The unfortunate fact USPO is overwhelmed with submissions & lacks the breadth of technical experts makes for strange decisions!

The method of coils/magnets arose back in the days when so called 'single domain' Neodymium-Boron Iron magnets could be made at more or less reasonable cost in almost any shape.

I recall the issue of patents and prior art also arose but nonetheless some magnetic shock absorbers were made which included the magnets as spring elements and other variations were brought to concept stage.

One wonders if patents are useful unless you are a drug or large s/w co.

Might design cycle, given more advanced tools, in market responsiveness not instead speed up so most patenting becomes unnecessary ?

Those ramp-type clutches aren't particularly reliable. They're the ones that fail in your car starter. The helical spring clutch would be superior in this (stupid) application.

Far better to have a magnetically damped magnet-in-coil system, which can also be tuned in action.

If you wonder about the amount of energy being dissipated, look at the finned reservoir above the main rear shock absorber on a modern motorcycle. The fins are there to dissipate the heat from the damping action of the shock absorber.

Are you implying that because rack and pinion gears can work for years in steering systems that they will work equally well in high frequency load bearing for a sizable amount of vehicle weight as a shock absorber ?

The forward voltage drop is significant when the output voltage of the device is small. This is a problem especially for linear generators because they need very strong magnetics or a lot of coil to ramp up the voltage. Small motor-generators also need to be spun fairly quickly to generate higher voltages.

E.g. with 12 volts AC, you get a 1.4 volt drop in the simple bridge rectifier, which causes a ~12% loss in efficiency.

It is understandable why they would make the argument for a different solution. What they propose instead just happens to be a bad idea for other reasons.

What the hell are you rambling about? Do you think I support the idea of a mechanical ratchet and brushes over a rectifier?

You have given the distinct impression rectifiers are & I quote "..a significant efficiency loss," as blanket generalisation.

I'm not arguing you're in favour of mechanics, I'm responding to your claim about rectifiers.

Your retort by association defence & I quote "..they need very strong magnetics or a lot of coil.." doesn't take into account a number of design parameters. A simple 'back of the envelope calc' & appropriate geometry shows 200-400V achievable.

Your 'education' about 12v is yet another example of BT in terms of dialectic. What sort of designer would use such a low voltage unless, they are attached to BT they cant look at alternate topology ?

Trying to justify your generalisation a bad design example is yet another example of BT but, this time of debating methodology.

Mike Massen, Isaacsname, you may be aware that his group developed magnets and coils based harvester two years ago.

Which makes me wonder how far & with what intellectual resources they 'developed' their design.

Justin284 may also not be aware of design politics

There must be a reason that they are moving from the magnets and coils to the mechanical motion rectifier.

Sadly, these changes in direction are occasionally political or at the behest of a stubborn or uneducated investor Eg. BMW developed cars that can reliably run on hydrogen, ie. nice grant from German govt !

In contrast, I had an investor ~15 yrs ago wanting a product with no moving parts, despite fact one such part & far less & simpler electronics made it more reliable & cheaper.

Some 2 years ago, he was upset to find a copy of his concept but with one moving part in USA.

Are you implying that because rack and pinion gears can work for years in steering systems that they will work equally well in high frequency load bearing for a sizable amount of vehicle weight as a shock absorber ?

No, I'm implying they are two entirely different systems, under two entirely different conditions. A rack and pinion steering system is not subject to the same physical stresses as a shock absorber. This idea is antiquated, at best, imo.

doesn't take into account a number of design parameters. A simple 'back of the envelope calc' & appropriate geometry shows 200-400V achievable.

Please show your calculations before making such claims. What are your assumptions about the generator? How big it is, how much wire can you fit in it, how strong are the magnets? How fast does it spin?

Your 'education' about 12v is yet another example of BT in terms of dialectic. What sort of designer would use such a low voltage unless, they are attached to BT they cant look at alternate topology ? Trying to justify your generalisation a bad design example is yet another example of BT but, this time of debating methodology.

The fact of the matter is, that the device has to work over a range of frequencies. Low frequency vibration translates directly to slow rotation speed of the generator, which translates directly to low output voltage.

Your method of discussion is bordering incomprehensible, yet you accuse others of "BT"

Besides. There are active rectifiers with virtually no forward voltage drop using FETs instead of diodes, and they are usually employed when you have to deal with AC/DC and DC/DC conversions at low voltages.

The only reason I'm talking about diodes in the first place is because the article mentions diodes.

@IsaacsnamePiezo as is used in gas lighters etc might be of use but high voltage pulses generally, difficult to handle and not comparably efficient to magnetics in this application. Link is of interest, thanks

@EikkaSo you want me to educate you & give free electronic engineering advice based upon 32 years experience & on a public forum ?Surely, this is another example of BT, or rather Sloppy Commercial Thinking (SCT) ?You've discovered synchronous rectification great, then your BT generalisation, I quote you "..a significant efficiency loss," is not valid.

Article talks as if rectifiers/caps are bad, which is a type of spin, ie. The writer is attempting to manipulate the readers to suggest mechanics are somehow an improvement, sad that some cant see this.

Sorry you don't understand what I'm talking about & sorry English isn't your first language, suggest re-read the article and comments slowly & see precisely what I am saying, that's all from me on this topic :-)

The idea is good but the machine is too expensive and subject to wear out quickly. A linear stepping motor will work as a generator is this application and only has the magnet stack as the only moving part with zero wear or friction that generates heat and wastes energy.

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